In the manufacture of patterned devices and especially microelectronic devices, the processes of etching different layers which constitute the finished product are among the most crucial steps involved. One method widely employed in the etching process is to overlay the surface to be etched with a suitable mask.
The mask is typically created by imagewise forming a pattern of resist material over those areas of the substrate to be shielded from the etching. The resist is normally formed of a polymeric organic material. The pattern is formed by imagewise exposing the resist material to irradiation by lithographic techniques. The irradiation employed is usually x-ray, UV radiation, electron beam radiation or ion-beam radiation.
Radiation sensitive materials and/or compositions are either positive-acting (i.e. radiation solubilizable) or negative-acting (i.e. radiation insolubilizable or radiation crosslinkable). Positive-working (radiation) sensitive compositions are rendered soluble (or developable) by actinic radiation (deep-near UV, x-ray, electron-beam or ion-beam) and can be removed using selective developing solutions leaving unexposed areas intact. Negative-working (radiation) sensitive compositions are those which become insoluble upon exposure to actinic radiation. Selected solutions can dissolve and remove the unexposed areas of the composition while leaving the exposed portions intact. Development of such exposed materials yields negative tone images.
After the resist is developed forming the desired mask, the substrate and mask can be immersed in a chemical solution which attacks the substrate to be etched while leaving the mask intact. These wet chemical processes suffer from the difficulty of achieving well-defined edges on the etched surfaces. This is due to the chemicals undercutting the mask and the formation of an isotropic image. In other words, conventional chemical wet processes do not provide the resolution considered necessary to achieve optimum dimensions consistent with current processing requirements.
Moreover, such wet etching processes are undesirable because of the environmental and safety concerns associated therewith.
Accordingly, various so-called "dry processes" have been suggested to improve the process from an environmental viewpoint, as well as to reduce the relative cost of the etching. Furthermore, these "dry processes" have the potential advantage of greater process control and higher aspect ratio images. Also, when fabricating patterns having feature sizes below 350 nm, dry etching processes are necessary for profile control.
Such "dry processes" generally involve passing a gas through a container and creating a plasma in this gas. The species in this gas are then used to etch a substrate placed in the chamber or container. Typical examples of such "dry processes" are plasma etching, sputter etching, and reactive ion etching.
Reactive ion etching provides well-defined, vertically etched sidewalls.
One of the challenges in the fabrication of microelectronic devices and masks is to develop a resist which exhibits good lithographic performance as well as high dry etch resistance for subsequent pattern transfer into an underlying substrate. The dry etch chemistries include O.sub.2 currently used for antireflective coatings, Cl.sub.2 /O.sub.2 currently used for chrome etching in mask fabrication, Cl.sub.2 based plasma for polysilicon etch, and fluorocarbon based plasmas such as CF.sub.4 for oxide etching. These plasmas are examples only and are not meant to limit the scope. Conventional novolak/diazonapthoquinone resists used for i-line lithography have to date exhibited the best dry etch resistance. ZEP is an e-beam resist which has been adopted by the industry for advanced mask making to replace the conventional wet etch polybutenesulfone (PBS) process. Although ZEP provides significant improvement over the PBS process, its dry etch resistance to Cl.sub.2 /O.sub.2 is marginal (etch rate of 1.95 nm/s). Novolac is 1.4 nm/s.
There is a need to develop radiation sensitive compositions that provide improved dry etch resistance for use in mask fabrication (binary, attenuating phase shift masks, alternating phase shift masks) and for device fabrication.
Further, the use of polyvinyl diphenylferrocene and polyvinylferrocene as negative resists in ion implantation masking and in the formation of conductive patterns has been suggested (see U.S. Pat. No. 3,885,076). It is stated that the electron beam causes crosslinking of these polymers and renders negative patterns. Other polymers containing metal groups are referred to in U.S. Pat. No. 4,156,745. Lead methacrylate, when incorporated into copolymers with methylmethacrylate increases the speed of the resist compared to homopolymers of methylmethacrylate. The use of polyvinylferrocene has been proposed for oxidative decomposition to iron oxide patterns according to U.S. Pat. No. 4,027,052. The pattern delineation is accomplished by applying x-rays. Moreover, silicon containing resists have been quite prevalent. The use of silicon and germanium has been intended to impart O.sub.2 etch resistance to the resist material. For example, see U.S. Pat. Nos. 4,764,247; 4,935,094 and 5,733,706, and Microelectronic Engineering 3,279 (1985). Nevertheless, the prior art does not disclose any organometallic polymeric materials for masking against Cl.sub.2 and Cl.sub.2 /O.sub.2 RIE (reactive ion etching).
Cl.sub.2 RIE and C.sub.2 /O.sub.2 RIE are used in the electronics industry in etching polysilicon and in etching chromium in optical mask fabrication. The etched patterns are differentiated from the unetched surface areas by a layer of resist material. The resist should have adequate resistance towards the particular plasma used in the etching. Cl.sub.2 /O.sub.2 plasma is regarded as one of the harshest environments to which a surface can be subjected. Examples of resists that are used for the above-mentioned applications are e-beam resists such as ZEP 7000 and ZEP 520 used for patterning chromium in the preparation of optical masks and copolymers of tert.-butyl methylacrylate, tert.-butyl methacrylic acid, and methylmethacrylate, experimental resists, referred to herein as "X-1", described in U.S. Pat. No. 5,071,730 and intended as a 193 nm UV resist. Other deep UV resists that are used for patterning in Cl.sub.2 /O.sub.2 plasma include UV2 and UV6. ZEP resist has the chemical formula 1 shown below. ##STR1##
The etch rate of ZEP in Cl.sub.2 /O.sub.2 plasma is 1.95 nm/sec compared to 1.40 nm/sec for Novolac. This rate is regarded as marginal. The structure of X-1 is shown below as formula 2. It also has a low resistance to Cl.sub.2 /O.sub.2 plasma because of the methacrylate backbone of the polymer. ##STR2##
Both ZEP and X-1 resists require an increase in their RIE resistance properties. Other commercial resists such as amplified resists (e.g. APEX E) for deep UV applications, could also benefit from a boost in their RIE resistance properties.